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While these values do not compute an age for the Earth, they do establish a lower limit (the Earth must be at least as old as any formation on it).This lower limit is at least concordant with the independently derived figure of 4.55 billion years for the Earth's actual age.The most direct means for calculating the Earth's age is a Pb/Pb isochron age, derived from samples of the Earth and meteorites.This involves measurement of three isotopes of lead (Pb-206, Pb-207, and either Pb-208 or Pb-204).Further, the processes of erosion and crustal recycling have apparently destroyed all of the earliest surface.The oldest rocks which have been found so far (on the Earth) date to about 3.8 to 3.9 billion years ago (by several radiometric dating methods).Helium is not light enough to escape the Earth's gravity (unlike hydrogen), and it will therefore accumulate over time.The current level of helium in the atmosphere would accumulate in less than two hundred thousand years, therefore the Earth is young.
If the solar system formed from a common pool of matter, which was uniformly distributed in terms of Pb isotope ratios, then the initial plots for all objects from that pool of matter would fall on a single point.he generally accepted age for the Earth and the rest of the solar system is about 4.55 billion years (plus or minus about 1%).This value is derived from several different lines of evidence.Over time, the amounts of Pb-206 and Pb-207 will change in some samples, as these isotopes are decay end-products of uranium decay (U-238 decays to Pb-206, and U-235 decays to Pb-207).
This causes the data points to separate from each other.
Some of these rocks are sedimentary, and include minerals which are themselves as old as 4.1 to 4.2 billion years.